"DBRS would expect Danske to receive a large fine given the prolonged period of time and the very high estimated amount of money transferred through the non-resident portfolio in Estonia," the rating agency said in a statement.

"A substantial fine, especially if accompanied by weakening in investor confidence, could lead to negative rating pressure," it said.

DBRS has an 'A'-rating on Danske Bank's long-term issuer rating. (Reporting by Jacob Gronholt-Pedersen; editing by John Stonestreet)